1. Field of the Invention
The present invention relates to a filter for removing noise, and more particularly, to a filter for removing noise that can improve performance and capacity by implementing high common-mode impedance in the same frequency and improving insertion loss and reduce manufacturing costs and improve productivity by simplifying structures and processes.
2. Description of the Related Art
Electronic products, such as digital TVs, smart phones, and notebook computers, have functions for data communication in radio-frequency bands. Such IT electronic products are expected to be more widely used since they have multifunctional and complex features by connecting not only one device but also USBs and other communication ports.
Here, for higher-speed data communication, data are communicated through more internal signal lines by moving from MHz frequency bands to GHz radio-frequency bands.
When more data are communicated between a main device and a peripheral device over a GHz radio-frequency band, it is difficult to provide smooth data processing due to signal delay and other noises.
In order to solve the above problem, an EMI prevention part is provided around the connection between an IT device and a peripheral device. However, conventional EMI prevention parts are used only in limited regions such as specific portions and large-area substrates since they are coil-type and stack-type and have large chip part sizes and poor electrical characteristics. Therefore, there is a need for EMI prevention parts that are suitable for slim, miniaturized, complex, and multifunctional features of electronic products.
A common-mode filter of EMI prevention coil parts, that is, filters for removing noise in accordance with the prior art is described below in detail with reference to FIGS. 1 to 3.
As shown in FIG. 1, a conventional common-mode filter includes a first magnetic substrate 1, an insulating layer 2 provided on the first magnetic substrate 1 and including a first coil pattern 2a and a second coil pattern 2b which are vertically symmetrical to each other, and a second magnetic substrate 3 provided on the insulating layer 2.
Here, the insulating layer 2 including the first coil pattern 2a and the second coil pattern 2b is formed on the first magnetic substrate 1 through a thin-film process. An example of the thin-film process is disclosed in Japanese Patent Application Laid-open No. 8-203737.
And, the second magnetic substrate 3 is bonded to the insulating layer 2 by an adhesive layer 4.
Further, an external electrode 5 is provided to surround both ends of a laminate including the first magnetic substrate 1, the insulating layer 2, and the second magnetic substrate 3, and the external electrode 5 is electrically connected to the first coil pattern 2a and the second coil pattern 2b through the drawn lead wire (not shown).
In the conventional common-mode filter configured as above, the first coil pattern 2a and the second coil pattern 2b are configured to vertically face each other to remove common-mode noise and smoothly pass a differential-mode signal.
More specifically, as shown in FIG. 2, the common-mode noise can't pass through the filter since magnetic fluxes generated by the current flow of the first coil pattern 2a and the second coil pattern 2b reinforce each other to have high impedance, and the differential-mode signal can smoothly pass through the filter since the magnetic fluxes offset each other.
However, in the conventional common-mode filter, as the frequency increases, the differential-mode impedance also increases, thus causing insertion loss.
That is, as the magnetic fluxes flowing between the first coil pattern 2a and the second coil pattern 2b reinforce each other and the frequency increases, the differential-mode impedance also increases, thus increasing the insertion loss.
Especially, the larger the interval between the first coil pattern 2a and the second coil pattern 2b, the higher the differential-mode impedance and the insertion loss. Accordingly, characteristics of the common-mode filter are further deteriorated.
Further, in the conventional common-mode filter, the second magnetic substrate 3 is bonded to the insulating layer 2 by the adhesive layer 4, a magnetic flux flow is further disrupted by non-magnetic characteristics of the adhesive layer 4, thus causing rapid deterioration of characteristics.
In order to overcome the above problem, although it is possible to increase the length of the first coil pattern 2a and the second coil pattern 2b, in such a case, there are disadvantages such as an increase in manufacturing costs of the filter for removing noise and an increase in size of the filter for removing noise.